The invention relates to the technical field of walk-assist robots and especially relates to a pumpless hydraulic walk-assist robot and a control method thereof. The robot comprises a support mechanism, an adjusting mechanism and an oil-way pipeline; the support mechanism comprises a thigh housing, a shank housing, a connecting plate and a sole plate; the adjusting mechanism comprises a hydrauliccylinder; two ends of the hydraulic cylinder are hinged to the thigh housing and the shank housing; the hydraulic cylinder comprises a cylinder body and a piston rod; the piston of the piston rod divides the chamber inside the cylinder into a first chamber and a second chamber; the oil-way channel comprises a first oil way and a second oil way; the first oil way and the second oil way can be connected with the first chamber and the second chamber respectively; the first oil way and the second oil way can both be connected to the oil box; the first oil way is connected with an energy storage tank which provides thrust to the bottom of the piston. The invention provides a pumpless hydraulic walk-assist robot and a control method thereof, which have low energy consumption, can accurately judge the movement state of legs, passively cooperate with the walking state of the human body, and ensure the stability of the walking process.